Enhancement of Wear Resistance of Copper With Tungsten Addition $(≤20wt%)$ by Powder Metallurgy Route

Copper–tungsten composite materials are developed for applications such as electrical contacts, resistance electrodes, and contact tips in welding guns as well as for components requiring higher wear resistance. In addition to the aspect of improved performance, it is scientifically interesting to assess the tribological properties, and therefore the objectives of the present work include, to determine the role of W additions in improving the fretting wear resistance of Cu for electrical applications, to determine the optimum concentration for W additions, and to identify the mechanisms responsible for fretting wear improvements. In addressing these issues, a planned set of fretting wear tests were conducted on powder metallurgically processed Cu–W composites (maximum W content of $20wt%$⁠) against steel counterbody under varying load (up to 10 N) for 10,000 cycles. It has been observed that at lower loads of 2 N, the coefficient of friction (COF) recorded was $∼0.9$ for the $Cu–20wt%W$/steel, whereas it was $∼0.85$ for a pure Cu/steel couple. Under similar operating conditions with the increase in load, the COF decreases to 0.5 at 10 N load, irrespective of the composition of the Cu–W composite. Furthermore, the incorporation of $5wt%W$ has reduced the volumetric wear loss by 4–6 folds in comparison to unreinforced Cu. The addition of even higher percentage of W has led to increase its wear resistance by $∼10$ folds. Under the investigated conditions, the wear rate systematically decreases with the increase in load for all the tested Cu–W composites. Based on the topographical observation of worn surfaces, it is observed that wear mechanisms for the Cu and Cu–W composites are tribochemical wear, adhesive wear, and abrasive wear. The incorporation of harder W particles (⁠$5wt%$ or more) help in abrading the steel ball and in forming a dense tribolayer of $FexOy$⁠, which effectively reduces wear rate and hence, increases wear resistance of the Cu–W composite surface in reference to unreinforced Cu.